Field of the Invention
The present invention relates to a transdermal absorption sheet and a method for manufacturing the transdermal absorption sheet and in particular, to a technique for concentrating a drug at microneedles.
Description of the Related Art
Conventionally, methods for administering a medicine (drug) or the like through a biological surface, that is, the skin or mucosa mostly involve attaching mainly an aqueous material or a powdery material. However, since an attachment area for these materials is limited to the surface of the skin, perspiration, contact with foreign matter, or the like may cause the attached medicine or the like to be removed, and administering an appropriate amount of medicine is difficult. Furthermore, in allowing the medicine to permeate deep through the skin, it is difficult to reliably control a depth of penetration using a method that utilizes permeation by diffusion of a medicine as described above. Thus, obtaining sufficient drug efficacy has been difficult.
Because of such a situation, a method has been carried out in which a transdermal absorption sheet provided with microneedles (needle-like protruding portions) having a high aspect ratio and containing a drug is used to inject a medicine through the microneedles inserted into the skin. In order to make the transdermal absorption sheet available, the drug needs to be mixed into the transdermal absorption sheet. However, drugs are expensive in many cases, and thus, the drug needs to be contained in the transdermal absorption sheet so as to concentrate at the microneedles.
A method for manufacturing a transdermal absorption sheet is described in, for example, Japanese Patent Laid-Open No. 2010-69253 (Patent Literature 1) and Japanese Patent Laid-Open No. 2008-194288 (Patent Literature 2).
Patent Literature 1 discloses a manufacturing method for a transdermal absorption sheet which involves feeding and solidifying a material solution containing a drug in a mold in which inverted shapes of microneedles are formed and then feeding and solidifying a material solution containing no drug in the mold. According to Patent Literature 1, this allows the drug to efficiently concentrate at the microneedle.
Patent Literature 2 is not a technique for efficiently concentrating the drug at the microneedles but is a technique for improving sustained release of the drug. According to Patent Literature 2, needle-like components are manufactured as follows. That is, Patent Literature 2 discloses a method for manufacturing needle-like components by applying an easily decomposable material to a substrate, then selectively applying a projecting portion material only to a portion corresponding to needle-like recessed portions of the mold or applying the projecting portion material all over the mold to obtain a coating layer, then pressing a recessed plate provided with inverted shapes of needle-like protruding portions against the coating layer, and thereafter peeling the recessed plate off from the substrate. According to Patent Literature 2, this enables transdermal administration with sustained release and needle-like components with a sufficient mechanical strength can be manufactured.